WO2011158118A2 - Procédé et dispositif de formation d'une configuration de contact électrique sur une photopile - Google Patents

Procédé et dispositif de formation d'une configuration de contact électrique sur une photopile Download PDF

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Publication number
WO2011158118A2
WO2011158118A2 PCT/IB2011/001736 IB2011001736W WO2011158118A2 WO 2011158118 A2 WO2011158118 A2 WO 2011158118A2 IB 2011001736 W IB2011001736 W IB 2011001736W WO 2011158118 A2 WO2011158118 A2 WO 2011158118A2
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WO
WIPO (PCT)
Prior art keywords
solar cell
contact pattern
heating
electrical contact
etching paste
Prior art date
Application number
PCT/IB2011/001736
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English (en)
Other versions
WO2011158118A3 (fr
Inventor
Chetan Singh Solanki
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Indian Institute Of Technology
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Publication date
Application filed by Indian Institute Of Technology filed Critical Indian Institute Of Technology
Publication of WO2011158118A2 publication Critical patent/WO2011158118A2/fr
Publication of WO2011158118A3 publication Critical patent/WO2011158118A3/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to solar cells and more particularly, to formation of current carrying electrical contact patterns on the solar cells. DESCRIPTION OF THE BACKGROUND ART
  • Screen printing technology generally includes the steps of disposing a mesh designed in a shape of a finger-bus bar pattern on a front side of the solar cell. Thereafter, a metallic paste that includes a si lver powder, glass frits, and organics is applied over the mesh.
  • a metallic paste that includes a si lver powder, glass frits, and organics is applied over the mesh.
  • a lead borosilicate glass with high lead oxide content is used as glass frits whereas the organics comprises of a binder, solvent, and certain additives that ensures proper printing properties when applied on the solar cells.
  • the mesh is removed from the solar cell and the solar cell leaving behind the metallic paste in the form of a finger-bus bar pattern on an antireflective coating (usually SiNx, Silicon Nitride) provided on the top surface of the solar cell.
  • an antireflective coating usually SiNx, Silicon Nitride
  • the next step in screen printing technology involves, placing the solar cell with the metallic paste deposited thereon within an infra-red (IR) furnace operating at high temperatures. Thereafter, subjecting the solar cell to firing within the furnace for pattern formation and metal deposition on the formed pattern. The firing is generally carried out at high temperatures to the tune of 800°C- 900°C and for sufficient time to ensure proper etching and metal deposition.
  • IR infra-red
  • the glass frit plays the most important role as it etches the antireflective coating on the solar cell. Due to this etching, the silver powder and the organics, which are dried and burnt off, are deposited on the etched portions to enable formation of electrical contact for the solar cell. However, during metal deposition, some amount of glass frits are also accumulated along with the silver powder and organics on the solar cell within the etched portions. It is observed that these traces of glass frits affect the current transport from the semiconductor into the silver film to a great extent. Additionally, the glass also dissolves several percent of silver and enhances the sintering process of the fine silver powder during firing. Such unwanted deposition of the glass frits leads to porosity within the conductive metal contact formed on the solar cell that hinders flow of electric charge therein. Thus, current collecting capacity of the solar cells is compromised resulting in the overall efficiency to be on the lower side.
  • the method includes the steps of forming a pre-form of the electrical contact pattern on a top surface of the solar cell, thermosetting the pre-form contact pattern having a MERCK ISISHAPE etching paste disposed thereon to a temperature of about 390°C, and subjecting the solar cell to metallization process for deposition of metal on the etched contact pattern.
  • the step of forming pre-form of the electrical contact pattern on the top surface of the solar cell further includes applying the etching paste on the insulating layer, providing a heating device having a heating surface protruding outwardly from the heating device, the heating surface formed to have a shape similar to that of the electrical contact pattern, and contactably positioning the heating surface on the etching paste so that the heating surface forms a pre-form of the electrical contact pattern on the insulating layer.
  • the step of forming pre-form of the electrical contact pattern on the top surface of the solar cell further includes providing a heating device having a heating surface protruding outwardly from the heating device, the heating surface formed to have a shape similar to that of the electrical contact pattern, applying a layer of etching paste on the heating surface, and contactably positioning the heating surface having the etching paste applied thereto on the insulating layer of the solar cell.
  • the step of subjecting the solar cell to metallization process further includes deposition of Ni by electroless Ni plating technique a composition of NiCl 2 , NaP02H2-H20 and other chemicals on the etched electrical contact pattern.
  • a heating device connected to a temperature control unit and capable of forming a contact pattern on a solar cell when contacted and operated therewith includes a conductive base portion having a plurality of holes formed therein, a first heating member connected to one of the plurality of holes for providing necessary heating effect to the heating device, a sensor disposed within other of the plurality of holes for sensing temperature of the heating device and based on the sensed temperature sending signal to the temperature control unit, and a heating surface protruding outwardly from the base portion and having a shape representative of the electrical contact pattern.
  • FIG. 1 is a cross-sectional view of a solar cell used in various embodiments of the present invention.
  • FIG. 2 is a perspective view of a heating device according to an embodiment of the present invention.
  • FIG. 3 shows an electrical connection of the heating device of FIG. 2 with a temperature control unit
  • FIG. 4 shows application of an etching paste on the heating device of FIG. 2 according to one embodiment of the present invention
  • FIG. 5 shows the step where the heating device of FIG. 4 is about to be positioned on the solar cell of FIG. 1 ;
  • FIG. 6 shows the step where the heating device of FIG. 4 connected with the temperature control unit is contactably positioned over the solar cell of FIG. 1 ;
  • FIG. 7 shows an etched finger-bus bar pattern formed on the solar cell after completion of the etching process
  • FIG. 8 shows application of an etching paste on the solar cell of FIG. 1 according to one embodiment of the present invention
  • FIG. 9 shows an etching step carried on the solar cell of FIG. 8.
  • FIG. 10 shows an electro-less nickel plating technique for deposition of metal on the formed finger-bus bar pattern on the solar cell of FIG. 7, according to an embodiment of the present invention.
  • FIG. 1 shows a cross-sectional view of a solar cell 100 used in the various embodiments of the present invention described in the foregoing specification.
  • solar cells used in photovoltaic technologies are generally made from crystalline -silicon composite material and includes a P-type semiconductor, an N-type semiconductor, and an insulating layer.
  • the solar cell 100 as shown in FIG. 1 , has an N-type semiconductor 102 formed over a P-type semiconductor 1 04, and an insulating layer 106 disposed on the top of the N-type semiconductor 102.
  • the insulating layer 106 acts as an anti-reflective coating to the solar cell 100 that causes total internal reflection of the solar rays incident on the solar cell 100.
  • the insulting layer 1 06 is made from SiN x (Silicon Nitride).
  • the electric contact pattern may be formed to represent a shape of a finger-bus bar pattern well-known in the art, for carrying and distributing electric current from the solar cell 100 to an external load (not shown).
  • a bottom surface 108 of the P-type semiconductor 104 may also have an insulating layer 106 that may be subjected to chemical treatment/etching process simi lar to that provided on top of the N-type semiconductor 102 for forming similar or other designed electric contact patterns.
  • electric contact pattern formed only on the top of the solar cell 100 will be explained.
  • FIG. 2 shows a perspective view of a heating device 1 10 according to an embodiment of the present invention.
  • the heating device 1 10 has a flat base portion 1 12 made of a conductive material such various metallic materials known in the art. Further, the heating device 1 10 is micro- machined to have a heating surface 1 14 that extends upwardly from the base portion 1 12.
  • the heating surface 1 14 serves as an interface for heat transfer between the solar cell 100 and the heating device 1 10 when the heating device 1 10 contacts the solar cell 100.
  • edges 1 16 of the heating surface 1 14 are micro-machined to have a shape similar to that of the electrical contact pattern that is to be formed on the solar cell 1 00.
  • the heating surface I 14 of the heating device 1 10 is micro-machined to have a shape of a finger-bus bar pattern 1 18.
  • the base portion 1 12 has a plurality of holes 1 20 formed therein that extends from a first side 122 of the base portion 1 12 to an opposite second side 1 24 or, may stop along a certain distance before the opposite second side 124.
  • a first heating member 126 having a power rating of 150W, is disposed which when connected with a temperature control unit 130 (FIG. 3) provides the necessary heating effect to the base portion 1 1 2 as well as the heating surface 1 14.
  • a second heating element 130 disposed within a second hole 134.
  • a sensor 1 36 that senses temperature of the heating device 1 10 is also connected to a third hole 138 that is disposed in between the two heating elements.
  • Benefit of disposing the two heating elements with the sensor 136 positioned therebetween is two folds. First, the heating elements by virtue of their positioning within the base portion 1 12 uniformly heat the heating surface 1 14 to a pre-requisite temperature. Second, as the sensor 1 36 is symmetrically positioned in between the two heating elements, the sensor 136 accurately measures the temperature of the heating surface 1 14.
  • FIG. 3 shows an electrical connection 140 between the heating device 1 10 and the temperature control unit 130.
  • the sensor 136 senses the temperature of the heating device 1 10, it gives signal to the temperature control unit 130 and accordingly temperature of the heating element is regulated.
  • the heating surface 1 14 contacts an etching paste and transfers heat energy thereto so that the etching paste performs etching function.
  • the etching pastes are highly temperature sensitive and if not operated at their standard operating temperature, then the whole etching process may not function properly. Therefore, accurate measurement of the heating surface 1 14, provided by the above arrangement, becomes a must for such etching processes.
  • a chemical semi-molten etching paste 142 preferably that of M ERCK ISISHPETM is uniformly applied over the heating surface 1 14 of the heating device.
  • the etching paste 142 is uniformly applied over the edges 1 16 of finger-bus bar pattern 1 18 shape of the heating surface 1 14 so that the etching paste 142 also takes shape of the finger-bus bar pattern 1 18.
  • One method of applying the etching paste 142 over the edges 1 16 is to form this pattern on a thin sheet of plastic and then tightly positioning the plastic sheet on the edges 1 16 of the heating surface 1 14 so that the pattern of the etching paste 142 matches the finger-bus bar pattern 1 18 of the heating surface 1 14. In this manner, edges 1 16 of the heating surface 1 14 have the etching paste 142 adhered thereon.
  • other ways may be used to coat the etching paste 142 on the edges 1 16 of the heating surface 1 14 and be considered within the scope of the present invention. It will also be appreciated by a person skilled in the art that several other etching pastes operating at lower temperatures may be used in the various embodiments of the present invention and be considered within the scope of the present invention.
  • FIG. 5 shows the step where the heating device 1 10 electrically connected with the temperature control unit 130 (not shown) positioned adjacent to the insulating layer 106 of the solar cell 100.
  • the edges 1 16 of the heating surface 1 14 having the etching paste 142 coated thereon only contacts selective portions of a top surface 144 of the insulating layer 106. Quite clearly, these selective portions have an imprint of the shape of the finger-bus bar pattern 1 1 8 (not shown) of the heating surface 1 14. This leads to formation of a pre-form of the electrical contact pattern on the insulating layer 106.
  • This pre-form pattern acts as a guide pattern along which formation of 'final' electrical contact pattern on the solar cell 1 00 takes place when subjected to chemical treatment/etching process.
  • the temperature of the heating member is slowly raised and thermosetted to a temperature of about 390°C.
  • the pre-form of the electrical contact pattern is thermosetted at a temperature of 390°C. This allows the heating surface 1 14 to transfer heat to the etching paste 142 attached thereto and as a result of that the etching paste 142 is heated up.
  • the MERCK IS1SHPE 1 M etching paste 142 by virtue of its etching properties begins to perform its etching function at this temperature of 390°C. This marks the beginning of the etching step on the insulating layer 106 as described in the foregoing paragraphs.
  • the selective portions of the insulating layer 106 that are in physical contact with the etching paste 142 as well as available in the vicinity of the etching paste 142 are etched. As noted above, this etching is carried along the pre-form of the contact pattern acting as a guide pattern towards the top surface 146 (See FIG. 9) of the N-type semiconductor 102. Thermosetting of the pre-form with the etching paste 142 adhered to the heating surface 1 14 is allowed for approximately 90 seconds. Throughout this time period, all of the selective portions of the insulating layer 106 across its width (W) are etched thereby exposing a top surface 146 of the N- type semiconductor 102.
  • the exposed portions of the N- type semiconductor 102 corresponds to the final electrical contact pattern formed thereon.
  • the insulating layer 106 has developed cavities 148 (shown in FIG. 9) that have a shape similar to that of the pre-form of the electrical contact pattern.
  • the solar cel l 100 is thoroughly washed with known washing solutions for removing the untreated etching paste 142 and debris of the insulating layer 106.
  • a thoroughly washed solar cell 100 having the finger-bus bar electrical contact pattern is shown in FIG. 7.
  • the width of the finger that is obtained at the end of the above described etching process is 250 ⁇ ⁇ spacing.
  • This finger width of this dimension is achieved because of the fact that the thickness of the edges 1 16 of the heating surface 1 14 has a similar dimension. It will be understood by skilled person that a benefit of using the above explained heating device 1 1 0 is that width of the finger-bus bar pattern 1 1 8 is dependent on the width of the edges 1 1 6 of the heating surface 1 14 of the heating device 1 10. Thus, by controlling the width of the edges 1 16 one can very easily control the width of the finger-bus bar pattern 1 1 8 to be formed on the solar cell 100. Thus, finger widths of even lesser dimensions than that of 250 ⁇ may be easily achieved by varying the thickness of the edges 1 16 of the heating surface 1 14. Accordingly, the metal deposited on the etched electric contact pattern also has a smaller width and this provides some benefits over the known processes. For example, requirement of larger surface areas on the top of the solar cell 100 is reduced considerably resulting in overall efficiency of the solar cell 100 being increased. Another benefit is that the problem of recombination for charge carriers moving within the solar cell 100 is also reduced.
  • FIG. 8 illustrates another embodiment of the present invention. In this embodiment the
  • MERCK ISISUPETM etching paste 142 is applied on the top surface 144 of the insulating layer 106.
  • the etching paste 142 which is generally in sub-molten form, is uniformly applied over the insulating layer 106 by any device that is capable of uniformly applying such solutions over an even solid surface.
  • the heating device 1 10, as described above in various embodiments, having the heating surface 1 14 that has a shape of the electrical contact pattern is positioned on the solar cell 100.
  • the heating device 1 10 is positioned on top of the etching paste
  • the solar cell 100 and more particularly the formed electric contact pattern thereof is subjected to metallization process for deposition of metallic material thereon.
  • the metallization process is done through various well known metal deposition techniques.
  • FIG. 10 shows one embodiment of metal deposition technique according to the present invention in which metal is deposited by electroless nickel plating process.
  • the etched electric contact pattern is submerged into an electrolytic solution that had composition of a composition of NiCl 2 , NaP02H2 H2() and other chemicals.
  • the Electroless nickel (EN) plating is an auto-catalytic reaction used to deposit a coating of nickel chloride on a substrate.
  • the metallization on the etched electric contact pattern may also be done by well known thermal evaporation technique that requires similar lesser operating temperatures.
  • Al (Aluminum) metal is deposited on the bottom surface 108, i.e., bottom of the P-type semiconductor 104, in the finger-bus bar contact pattern for carrying electric current to an external load.
  • deposition of Al on the bottom surface 108 of the solar cell 100 in the above pattern may be carried by the above explained etching and metal deposition processes.
  • a I metal deposition on the bottom surface 108 of the solar cell 100 may also be carried by evaporation process.
  • the reason for using Al as metal is because of the fact that Al makes good ohmic contact with the silicon material of the P-type solar cell 100.

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  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Electrodes Of Semiconductors (AREA)
  • Photovoltaic Devices (AREA)

Abstract

La présente invention concerne un procédé de formation d'une configuration de contact électrique sur une photopile (100) comprenant les étapes consistant à former une préforme de la configuration de contact électrique sur une surface supérieure (144) de la photopile (100), à thermodurcir la configuration de contact de préforme sur laquelle est disposée une pâte pour gravure MERCK IS ISHAPE (142) à une température d'environ 390 °C, et à soumettre la photopile (100) à un processus de métallisation pour déposer du métal sur la configuration de contact gravée.
PCT/IB2011/001736 2010-06-14 2011-06-14 Procédé et dispositif de formation d'une configuration de contact électrique sur une photopile WO2011158118A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IN1787/MUM/2010 2010-06-14
IN1787MU2010 2010-06-14

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WO2011158118A2 true WO2011158118A2 (fr) 2011-12-22
WO2011158118A3 WO2011158118A3 (fr) 2012-03-01

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4307681A (en) * 1978-03-15 1981-12-29 Photon Power, Inc. Apparatus for quality film formation
US20060228897A1 (en) * 2005-04-08 2006-10-12 Timans Paul J Rapid thermal processing using energy transfer layers
US20090126788A1 (en) * 2006-03-01 2009-05-21 Sanyo Electric Co., Ltd. Solar cell and solar cell module including the same
US20090139568A1 (en) * 2007-11-19 2009-06-04 Applied Materials, Inc. Crystalline Solar Cell Metallization Methods
US20090302001A1 (en) * 2006-12-05 2009-12-10 Nano Terra Inc. Method for Patterning a Surface
US20100068889A1 (en) * 2006-11-01 2010-03-18 Merck Patent Gmbh Particle-containing etching pastes for silicon surfaces and layers

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4307681A (en) * 1978-03-15 1981-12-29 Photon Power, Inc. Apparatus for quality film formation
US20060228897A1 (en) * 2005-04-08 2006-10-12 Timans Paul J Rapid thermal processing using energy transfer layers
US20090126788A1 (en) * 2006-03-01 2009-05-21 Sanyo Electric Co., Ltd. Solar cell and solar cell module including the same
US20100068889A1 (en) * 2006-11-01 2010-03-18 Merck Patent Gmbh Particle-containing etching pastes for silicon surfaces and layers
US20090302001A1 (en) * 2006-12-05 2009-12-10 Nano Terra Inc. Method for Patterning a Surface
US20090139568A1 (en) * 2007-11-19 2009-06-04 Applied Materials, Inc. Crystalline Solar Cell Metallization Methods

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
M. BAHR ET AL.: 'A new approach for the front side metallization of industrial type silicon solar cells using a structurization by etching' PROCEEDINGS OF THE 22ND EUROPEAN PHOTOVOLTAIC SOLAR ENERGY CONFERENCE, [Online] 03 September 2007, MILAN, ITALY, Retrieved from the Internet: <URL:http://www.ferro.com/non-crns/ems/Sola r 2010/technical/2D0_2 2.pdf> [retrieved on 2011-12-12] *

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